Write the Change as Numbered Steps, Not Background Knowledge
Water-change instructions for an aquarium sitter should read like a recipe, because the reader may never have kept fish. Number the steps in the order they happen at the tank: switch off the heater and filter, siphon out water down to the tape mark you placed on the glass, refill slowly with the prepared water, switch everything back on, then watch the filter restart. State the amount in bucket terms the sitter can verify, such as two full marked buckets out and two back in, rather than fractions of a tank they cannot measure. Leave the written sheet at the tank with the equipment gathered beside it, so following the instructions never becomes a scavenger hunt through your cupboards.
Specify the Water Itself: Temperature, Conditioner and Source
The paragraph that protects the fish most is the one about the replacement water, so write it in full. Tell the sitter to use only the water you prepared and labelled, or, if they must prepare more, to treat fresh tap water with the named conditioner in the container provided and let it stand until it feels the same temperature as the tank against the inside of the wrist, checking with the spare thermometer if unsure. Forbid the shortcuts by name: no untreated tap water, no hot tap water to speed warming, no kettle water, and nothing carried in a bucket that has ever held cleaning products. Dedicate one marked bucket to the aquarium and say so, because detergent residue harmless to a floor is a genuine threat in a fish tank.
Cover the Siphon, the Substrate and the Fill Line
Describe the physical technique briefly and concretely: start the siphon as you have shown or described, hover it just above the gravel to lift waste without excavating the bed, and move slowly so the fish can drift away rather than being chased around their own home. Name the areas to concentrate on, usually the front corners and around feeding spots where debris gathers, and the areas to leave alone, such as planted roots. Refilling deserves its own sentence: pour over a plate, jug or the sitter's cupped hand to break the fall, stop at the fill line marked on the glass, and leave the lid and lights as they were found. A calmer refill keeps both the aquascape and the fish settled.
Build In the Restart Checks and the Reporting Habit
More holiday damage follows a water change that was never verified than follows the change itself, so instruct the sitter to stay for the restart. The filter must be humming with water moving at the outlet, the heater light should cycle, and no fitting should drip onto the cabinet or floor. Ask for a photo of the tank once finished and a message confirming the change is done, with the thermometer reading included, so you can spot a problem from a distance while it is still small. Tell the sitter what can wait and what cannot: a slightly cloudy tank an hour later usually settles, while a silent filter, a cracked-looking waterline drop or fish gasping at the surface earns an immediate call.
Make the Sheet a Permanent Handover Document
Once a sitter has successfully followed your sheet, keep that version, because it has been field-tested by exactly the audience it is written for. Update it when equipment changes, when the marked amounts shift with a new tank, or when a step confused its reader, and throw away older copies so nobody follows a superseded routine. Storing the proven sheet in your KinsLe Care Pass hands any trusted sitter temporary, clear access to your water-change steps, from the tape mark to the restart check, and turns a favour into a reliable piece of your fish's care.